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Three Reasons Why People Think Flu Shots Cause the Flu

“I got the flu shot, and it gave me the flu.” I wish that, as a physician, I had a dime for every time someone has said that to me. I would be a rich man.
The truth is, you cannot get influenza—the flu—from the flu shot. Never. No way. Not possible. The flu shot is made from killed flu viruses. Dead viruses cannot replicate and grow inside the body, and, therefore, they cannot cause the flu. These dead viruses do, however, cause the body to make anti-flu antibodies, and this is how the vaccination works. The body builds up antibodies—immunity—to the flu.
So, why do so many people insist that the flu shot causes the flu? There are, I think, three reasons for this.
1.) The flu shot can cause some mild flu-like symptoms. About 1% of people who receive the flu vaccine get a low-grade fever, a headache, and mild body aches after getting vaccinated. These are side effects of the vaccine. People, not unreasonably, often interpret these mild symptoms as “the flu.” In truth, these side effects are nothing like getting the real flu. The real flu makes you feel quite miserable: high fevers, chills, severe body aches, muscle aches, profound generalized weakness in addition to headache, cough, sore throat, stuffy nose, and red/watery eyes. Flu vaccine side effects rarely last more than a day, whereas the real flu usually lasts five to ten days.
2.) You can still get the flu after getting the flu shot. There are two ways this can happen. First, the flu shot takes about two weeks to start working. It takes two weeks to build up those immunizing antibodies. Thus, if you’re exposed to the flu within two weeks following the shot, you can still get the flu. And, if this happens, it’s very natural to think the flu came from the flu shot, itself. But, this is not the case. You were simply unlucky. You caught the flu before the shot could make you immune.
Secondly, the flu shot is not 100% effective. Depending on the year and the strain of flu going around, the shot is anywhere from 50-90% effective. This means that 10 to 50% of the time the shot doesn’t work. Some people will think the shot must have caused the flu, since they got the shot and still got the flu. But, the truth is, the shot simply didn’t give full immunity. Luckily, if you do get the flu after the flu shot, you are likely to have a milder course of flu than if you didn’t get the shot.
3.) Finally, the flu shot does not protect you against cold viruses. The shot only protects against the influenza virus. There are still dozens of cold viruses floating around out there. Consequently, if you catch a cold a few days after getting the flu shot, you might well think the shot gave you “the flu” because cold symptoms are similar to flu symptoms. (Cold symptoms, however, tend to be milder than flu symptoms: cough, sore throat, and runny nose, yes—but with less high fever, body aches, muscle aches, weakness, and generally feeling like crap.)
So, given these reasons why you might think you got the flu from the flu shot, why get the shot in the first place? For anyone who’s ever had a case of bona fide flu—as I have—the answer is pretty easy: the flu sucks. It’s rather like having a high fever plus profound fatigue plus a bad cold all associated with the feeling of having been run over by a Mack truck. Not fun. The flu shot can prevent a week of genuine misery, and, for me, that alone is worth a shot in the arm.
In addition, getting the flu shot could prevent you from getting the flu plus a flu-related complication such as pneumonia or a sinus infection. It could even prevent you from becoming a flu statistic. About 25,000 people (on average) die of flu-related complications each year in the United States (worldwide, there are 200,000 to half a million flu-related deaths).
Or, if you don’t want to get the flu shot to protect yourself, you might consider being a hero and getting it to protect others. One person with the flu can infect dozens of other people. So even if you don’t mind getting the flu, yourself, think about getting the flu shot in order to protect your friends, family members, and other close contacts from getting the flu from you.


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